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Virtually everything astronomers know about objects outside the solar system is based on the detection of photons-quanta of elec

admin2013-06-10  57
问题     Virtually everything astronomers know about objects outside the solar system is based on the detection of photons-quanta of electromagnetic radiation. Yet there is another form of radiation that permeates the universe: neutrinos. With (as its name implies) no electric charge, and negligible mass, the neutrino interacts with other particles so rarely that a neutrino can cross the entire universe, even traversing substantial aggregations of matter, without being absorbed or even deflected. Neutrinos can thus escape from regions of space where light and other kinds of electromagnetic radiation are blocked by matter. Not a single, validated observation of an extraterrestrial neutrino has so far been produced despite the construction of a string of elaborate observatories, mounted on the earth from Southern India to Utah to South Africa. However, the detection of extraterrestrial neutrinos are of great significance in the study of astronomy. Neutrinos carry with their information about the site and circum stances of their production; therefore, the detection of cosmic neutrinos could provide new information about a wide variety of cosmic phenomena and about the history of the universe.
    How can scientists detect a particle that interacts so infrequently with other matter? Twenty-five years passed between Pauli’s hypothesis that the neutrino existed and its actual detection; since then virtually all research with neutrinos has been with neutrinos created artificially in large particle accelerators and studied under neutrino microscopes. But a neutrino telescope, capable of detecting cosmic neutrinos, is difficult to construct. No apparatus can detect neutrinos unless it is extremely massive, because great mass is synonymous with huge numbers of nucleons (neutrons and protons), and the more massive the detector, the greater the probability of one of its nucleon’s reacting with a neutrino. In addition, the apparatus must be sufficiently shielded from the interfering effects of other particles.
    Fortunately, a group of astrophysicists has proposed a means of detecting cosmic neutrinos by harnessing the mass of the ocean. Named DUMAND, for Deep Underwater Muon and Neutrino Detector, the project calls for placing an array of light sensors at a depth of five kilometers under the ocean surface. The detecting medium is the sea water itself: when a neutrino interacts with a particle in an atom of seawater, the result is a cascade of electrically charged particles and a flash of light that can be detected by the sensors. The five kilometers of seawater above the sensors will shield them from the interfering effects of other high-energy particles raining down through the atmosphere.
    The strongest motivation for the DUMAND project is that it will exploit an important source of information about the universe. The extension of astronomy from visible light to radio waves to x-rays and gamma rays never failed to lead to the discovery of unusual objects such as radio galaxies, quasars, and pulsars. Each of these discoveries came as a surprise. Neutrino astronomy will doubtlessly bring its own share of surprises.
选项 A、get through,
B、pass by.
C、interact with.
D、derive from.
答案A
解析 本题问第一段第六行的"escape from"可用什么来代替。首段第四句谈到"Neutrinos can thus escape from regions of space where light...are blocked by matter"，由本句中的"thus"可知本句是承接上句内容而说的。而上句谈到"...even traversing substantial aggregations of matter，without being absorbed or even deflected"，也就是说中微子可以穿透物质，而不会被吸收，甚至不会偏斜。由此可以推出，第四句中"escape from"也是指从"regions of space"穿过去，丽光等电磁辐射却会被阻隔住(blocked)。故"穿过"正确。实际上中微子可以穿过物质(比如人体)，而光子等粒子则会被物质阻挡住，下文中谈到要对探测中微子的设备进行屏蔽，使其不受其他微粒子的影响，正是利用别的微粒子会被物质(比如海水)阻挡住，而中微子则会笔直穿过这一特性。绕过：强干扰项。文意是指中微子可以从物质中穿过(traversing)，而不是说遇到物质集团从旁边绕过去。相互作用：这里是指不与物质相互作用，而是从物质中间直接穿过去。源于：文中原意是说中微子能穿越空间，是因为它不受该空间内物质的束缚，而并非是"起源"于该物质。
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